1. Field of the Invention
The present invention relates to electronics and, more specifically but not exclusively, to switched-mode power converters.
2. Description of the Related Art
This section introduces aspects that may help facilitate a better understanding of the invention. Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is prior art or what is not prior art.
Switched-mode DC-DC power converters, often powered by rectified DC from AC mains, are ubiquitous as plug-in adapters used to power a plethora of electronic devices.
A typical such converter is copiously documented in the Power Integrations Design example report DER-227. Such converters are also taught in U.S. Pat. No. 4,459,651 and U.S. Patent Application Publication Nos. 2011/0026277 A1 and 2011/0018590 A1. Such converters typically generate commutation pulses on the mains side of galvanic isolation circuitry.
Some known converters use forms of absorption modulation to convey feedback information through the power transformer. In U.S. Pat. No. 8,000,115, a temporary decrease in the loading of a transformer secondary winding during a flyback pulse generates a corresponding voltage disruption of the same pulse, which disruption is detected on another transformer winding to effect primary-winding-side converter control. In U.S. Pat. No. 5,973,945, a similar method is taught, but instead of unloading a flyback pulse, temporary loading of a forward power pulse is taught. The circuitry for extracting the resulting information-bearing current disruption in the transformer primary circuit is quite involved. A similar absorption modulator is taught in U.S. Pat. No. 4,996,638.
Converters are also known wherein an analog voltage reflection of the converter output voltage seen on a primary-side winding is processed to generate a primary-side analog feedback signal which is used to control the commutating signals applied to the commutating switch to regulate converter output on its secondary side. Such feedback methods are taught in U.S. Pat. Nos. 4,597,036 and 3,889,173. Such methods are becoming less common due to the difficulty of reliably processing the analog information reflected into a primary-side winding to obtain an accurate feedback signal.
U.S. Pat. No. 4,937,727 teaches a mains-side pulse generator that is pulse-width controlled by a voltage-responsive clamp on the output side of a galvanic isolation barrier.